The response of a membrane inlet ion mobility

Abstract

The negative mode response of a membrane inlet ion mobility spectrometer, interfaced to an Extrel-C150 mass spectrometer, to chlorine in dry air over the range of concentrations 0–200 mg m⁻³ was characterised. Three distinct product ions were observed: an assembly of [Cl₂(H₂O)_n]⁻ and [Cl(H₂O)_n]⁻ entities with a reduced mobility of 2.19 cm² V⁻¹ s⁻¹, a carbon dioxide based cluster, [Cl₂(CO₂)(H₂O)₃]⁻ with a reduced mobility of 1.93 cm² V⁻¹ s⁻¹ and a dimer product thought to be [(Cl₂)₂(H₂O)]⁻ with a reduced mobility of 1.70 cm² V⁻¹ s⁻¹. The response to chlorine was found to be sensitive with a limit of detection significantly less than 1 mg m⁻³. Further exposures to chlorine were also undertaken with 5 and 10% by mass of water added to the adsorbent traps used to purify the drift and source gases within the instrument. This was done to simulate ageing of the air purification media. No changes in the chemistry of the product ions were observed with increasing levels of water contamination of the adsorbent media. The sensitivity was reduced and the observed drift times increased with increasing levels of water contamination with the reduced mobilities for the three product ion groups above found to vary across the ranges: 2.10–2.19, 1.84–1.93 and 1.66–1.70 cm² V⁻¹ s⁻¹, respectively.